Field of the Invention
The present invention relates to a swash plate type hydraulic pump including a swash plate that can be installed obliquely inclined relative to a rotational shaft and a plurality of pistons whose axial displacement is defined by the swash plate and that rotate around the rotational shaft.
Description of Related Art
Conventionally, a swash plate type hydraulic pump is known that includes a swash plate that can be installed obliquely inclined relative to a rotational shaft, and a plurality of pistons whose axial displacement is defined by the swash plate and that rotate around the rotational shaft. A hydraulic pump such as the one mentioned above is disclosed in the article entitled “VARIABLE DISPLACEMENT PISTON PUMP-P**V SERIES”, which is published on the website of TOKYO KEIKI INC. In the case of the hydraulic pump disclosed in the aforementioned article of TOKYO KEIKI INC., a cylinder block that rotates with a rotational shaft receiving input of torque is provided with a plurality of cylinder chambers extending parallel to the rotational shaft. Also, a plurality of pistons are supported relative to the respective cylinder chambers such that the pistons can be slidably displaced along a direction parallel to the rotational shaft. Note that the above-described article of TOKYO KEIKI INC. is published on the Internet at the URL “http://www.tokyo-keiki.co.jp/hyd/j/products/pdf/a_002-005.pdf”.
In the case of the above-described hydraulic pump, oil is sucked into the cylinder chambers while the cylinder block makes a half rotation, the pressure of the oil is raised in the cylinder chambers while the cylinder block makes a further half rotation, and the oil is discharged. Then, the pressure oil discharged from the hydraulic pump will be supplied to various devices. Further, a shoe structure that slides against the swash plate is provided at the end portions of the pistons of the above-described hydraulic pump. With the provision of this shoe structure, the above-described hydraulic pump is configured such that the pistons can slide against the swash plate installed in the housing in a state in which it is obliquely inclined relative to the rotational shaft.
Note that JP 2008-249099A discloses, as a mechanism of a type completely different from a hydraulic pump that supplies pressure oil to various devices, a motorcycle hydrostatic continuously variable transmission configured by connecting a swash plate type plunger hydraulic pump with a swash plate type plunger hydraulic motor via a hydraulic closed circuit. This hydrostatic continuously variable transmission is configured to perform lockup by closing the hydraulic closed circuit when the amount of the oil flowing from the hydraulic pump to the hydraulic motor is decreased in accordance with the variable control of the inclination angle of the swash plate of the hydraulic motor such that the input rotation of the hydraulic pump and the output rotation of the hydraulic motor are substantially synchronous.
Further, in the hydraulic pump of the above-described hydrostatic continuously variable transmission, the torque that is output from the engine is input to a pump casing (20) via a gear. Also, a swash plate (pump swash plate member 21), a pump cylinder (22), and a plurality of pistons (pump plungers 23) are disposed inside the pump casing. The swash plate is installed so as to be rotatable relative to the pump casing in a state in which the swash plate is inclined at a predetermined angle relative to the rotation center axis of the pump casing. The pistons are respectively disposed in a plurality of cylinder chambers (pump plunger holes 22a) that are provided in the pump cylinder installed facing the swash plate.
Also, in the hydraulic pump of the above-described hydrostatic continuously variable transmission, the swash plate pivots as a result of the pump casing being rotatably driven by the torque from the engine, and the pistons reciprocate in the cylinder chamber in response to the pivot movement of the swash plate. Thereby, pressure oil is discharged to the hydraulic motor. In this hydraulic pump, in place of the shoe structure that slides against the swash plate, the end portions of the pistons fittingly engage with recessed portions formed in the swash plate. Thereby, this hydraulic pump is configured such that the pistons reciprocate in response to the pivot movement of the swash plate.